The invention relates to long-range optical devices. A long-range optical device can be a monocular or binocular telescope in the meaning of the present invention, in particular a pair of binoculars. In the case of a binocular telescope, the long-range optical device has two optical channels.
During the usage of a long-range optical device, for example, a pair of binoculars, perturbing movements of the housing of the long-range optical device have a negative effect on the image quality of the image seen by the user. The perturbing movements acting on the housing result in shaking of the image, which perturb the observation of an object or scenery.
The perturbing movements acting on the housing can have various causes, which differ with respect to their frequency spectrum.
One cause of perturbing movements is the trembling of hands during a freehand usage of the long-range optical device, i.e. a usage without support by a tripod or the like. Perturbing movements which are to be attributed to trembling hands, have a frequency spectrum which comprises frequencies from approximately above 4 to approximately 20 Hz. Perturbing movements in such a frequency range are also referred to in the present description as high-frequency perturbing movements.
A further cause of perturbing movements are external influences, for example, an oscillating or vibrating ground of a land, water, or air vehicle. Such perturbing movements can have a frequency spectrum which lies below the frequency spectrum of trembling hands, i.e. which can contain frequencies below 4 Hz to close to 0 Hz.
Perturbing movements which have a frequency spectrum below approximately 4 Hz are referred to in the present description as low-frequency perturbing movements.
FIG. 1 schematically shows the frequency spectrum of perturbing movements, which can act on a long-range optical device, i.e. on its housing. In FIG. 1, the amplitude A of the perturbing movements is plotted against the frequency f. The low-frequency frequency range is identified with fN and the high-frequency frequency range is identified with fH. The frequency f0 is to indicate the boundary between the low-frequency frequency range and the high-frequency frequency range here. It is obvious that the frequency f0 does not necessarily have to lie at 4 Hz, but rather can be in a range between approximately 2 Hz and approximately 5 Hz.
Intentional movements of the housing of the long-range optical device are to be differentiated from perturbing movements, i.e. during a pivot of the long-range optical device to cause the view through the long-range optical device to be swept or to track a moving object.
Movably supporting at least one optical element of the arrangement of optical elements so it is movable relative to the housing is known for image stabilization in the event of perturbing movements of the housing. In the long-range optical device known from the document DE 38 43 776 A1, this at least one optical element is the image inversion system. A passive stabilization system based on mass inertia is provided for the image inversion system. The stabilization system has, on the one hand, a spring joint, via which a carrier, to which the image inversion system is fixedly connected, is movably supported so it is movable relative to the housing, and, on the other hand, a damping member, which is implemented as an eddy current damping element and which also acts between the carrier and the housing. The spring joint has two rotational degrees of freedom, specifically one degree of freedom around a horizontal axis of the long-range optical device and one degree of freedom around the vertical axis of the long-range optical device.
The movable supporting and damping of the movement of the image inversion system relative to the housing cause perturbing movements acting on the housing to be transmitted in a reduced manner or not at all to the image inversion system, but rather for this to be held more or less in an idle position, whereby the image which is observed by the user is stabilized.
A passive stabilization system based on mass inertia may be represented according to FIG. 2 by a mechanical equivalent diagram. FIG. 2 shows a mechanical equivalent diagram of a passive stabilization system 200 based on mass inertia for an optical element 202. The optical element 202 is fastened on a carrier 204, which is in turn supported on a bearing 206, wherein a first restoring force 208 proportional to the displacement amplitude of the carrier 204 and a second restoring force 210 proportional to the displacement velocity act on the carrier. In the known long-range optical device, the function of the bearing 206 and the first restoring force 208 are fulfilled by the spring joint and the second restoring force 210 is fulfilled by the eddy current damping member.
In such passive stabilization systems based on mass inertia, it has been shown that they can stabilize the image particularly effectively against perturbing movements in the high-frequency target frequency range. A curve is shown in FIG. 3, which shows the dependence of the degree of stabilization S on the frequency f in the frequency range above 1 Hz of a long-range optical device, as is known from the prior art and which has a passive stabilization system, which is based on mass inertia. As shown in FIG. 3, in the known long-range optical device a degree of stabilization of above 80% is achieved at frequencies above 6 Hz, while the degree of stabilization drops significantly at lower frequencies, in particular 4 Hz or less. In other words, a passive stabilization system based on mass inertia is capable of offering effective image stabilization in the event of perturbing movements such as trembling hands, while effective image stabilization is not provided in the case of perturbing movements such as, for example, low-frequency moving grounds. The stabilization behavior above 1 Hz is not shown in FIG. 3.
The possibility does exist, in the case of a solely passive stabilization system based on mass inertia, to modify the manipulated variables of restoring force proportional to the displacement amplitude and restoring force proportional to the displacement velocity so that effective image stabilization is also made possible in the case of perturbing movements in the low-frequency frequency range. However, this is not desirable in every case, because then in the case of an intended pivot of the long-range optical device, it can occur that the field of vision does not instantaneously follow the pivot movement, which is also referred to as a “panning effect”. This effect results in irritation in the observer and would restrict the usage of the image-stabilized long-range optical device.
In contrast, those long-range optical devices are known, for example, from EP 0 834 761 A1, which have an active, electronically controlled stabilization system. Such active, electronic stabilization systems do also permit image stabilization in the event of perturbing movements in the low-frequency frequency range, but have the disadvantage that, on the one hand, they require a very large structural volume and are very costly, and, on the other hand, a current must also flow to operate the actuators, for image stabilization in the event of perturbing movements in the high-frequency frequency range, which are caused in particular by trembling hands. Since the energy of the movement of the active stabilization system increases approximately linearly with the frequency of the perturbing movement, the most energy is consumed in the high-frequency range. If the active stabilization system does not stabilize in this high-frequency range, the energy consumption is significantly reduced.